Method and apparatus for solar heating air in a forced draft heating system

ABSTRACT

A solar heating system for use in combination with a forced draft heating system for heating ventilation air of a building. The solar heating system includes a solar collector assembly for heating a liquid circulated through the assembly. The heated liquid is stored in an insulated storage tank where it can be circulated through a heat exchanger positioned in an air duct of the forced draft heating system as need to heat air flow through the duct. The use of a liquid as the heat transfer fluid and providing a storage facility for heated liquid permits the heating system to operate for a period of time after the sun sets or becomes ineffective in providing solar radiation until the heat stored in the liquid becomes exhausted. To increase the heat storage capacity of the liquid, one or more heat sinks can be utilized to absorb excess heat from the liquid and then transfer the absorbed heat back to the liquid when an opposite thermal gradient exists. Additionally, the heating system can recover waste heat from hot combustion gases exhausted from a fuel-fired forced draft heating system.

FIELD OF THE INVENTION

The present invention relates generally to heating of ventilation air ofa building, and more particularly, to solar heating of ventilation airin an existing forced draft heating system.

BACKGROUND OF THE INVENTION

In recent years, the cost of energy has increased substantiallyresulting in higher operation costs associated with heating a buildingincluding residential and commercial buildings a like. In the most seversituations, the increased costs have forced limited or no operation ofthe building heating systems. It is known that solar radiation can beused for heating such buildings and an example of such devices aredescribed in the following U.S. Pat. No. 6,880,553; 4,934,338;4,509,503; and 4,343,296.

While the devices heretofore fulfill their respective, particularobjectives and requirements, they do not provide a solar heating systemthat is used in combination with an existing forced draft heatingsystem, that can be easily installed in an existing forced draft heatingsystem without substantial modification of the forced draft heatingsystem, can be used alone or concurrently with the forced draft heatingsystem, which can recovery waste heat from a fuel-fired forced draftheating system and which remains to be effective for a period of timeafter the sun has set or the sun becomes ineffective in providing solarradiation, as such there exists and need for an improved solar heatingapparatus and method of using the same in a forced draft heating system,which substantially departs from the prior art.

SUMMARY OF THE INVENTION

The present invention, which will be described subsequently in greaterdetail, includes a heating system for installation in a forced draftheating system to heating air flow through the ducting of the forceddraft heating system. The heating system includes a solar collectorassembly for heating a liquid circulated through the assembly. Theheated liquid is stored in an insulated storage tank where it can becirculated through a heat exchanger positioned in an air duct of theforced draft heating system as need to heat air flow through the duct.The use of a liquid as the heat transfer fluid and providing a storagefacility for heated liquid permits the heating system to operate for aperiod of time after the sun sets or becomes ineffective in providingsolar radiation until the heat stored in the liquid becomes exhausted.To increase the heat storage capacity of the liquid, one or more heatsinks can be utilized to absorb excess heat from the liquid and thentransfer the absorbed heat back to the liquid when an opposite thermalgradient exists. Additionally, the heating system can recover waste heatfrom hot combustion gases exhausted from a fuel-fired forced draftheating system.

In general, in one aspect, a solar heating system for use with a forceddraft heating system for heating ventilation air of a building, wherethe forced draft heating system includes an air handler, a heat source,a return air duct, an air discharge duct and a thermostat that controlsthe operation or the forced heating system is provided. The solarheating system includes a solar collector assembly which heats a liquidas it is circulated therethrough by solar radiation; a fluid storagetank for containing a quantity of heat transfer fluid;

-   -   a first heat exchanger positionable in an air duct of the forced        draft heating system such that air flowing through the duct is        caused to flow across the first heat exchanger. The solar        collector assembly is in fluidic communication with the fluid        storage tank such that heat transfer fluid contained therewithin        can be circulated through the solar collector assembly and        returned to the storage tank. The first heat exchanger is in        fluidic communication with the fluid storage tank such that heat        transfer fluid contained therewithin can be circulated through        the first heat exchanger and returned to the storage tank. A        controller is operative to effect the circulation of the heat        transfer fluid through the solar collector assembly as a        function of a temperature differential between the heat transfer        liquid in the solar collector assembly and the heat transfer        liquid in the fluid storage tank. The controller is operative to        effect the circulation of the heat transfer fluid through the        first heat exchanger as a function of the temperature of the        heat transfer fluid in the fluid storage tank, the temperature        of the air to be heated, and the desired temperature of the air        to be heated.

In general, in another aspect, the solar heating system includes asecond heat exchanger positionable in the flow of hot combustion gasesexhausted by the heat source of the forced draft heating system, whereinsaid second heat exchanger is in fluidic communication with said fluidstorage tank such that the heat transfer fluid contained within saidfluid storage tank can be caused to circulate through said second heatexchanger and returned to said fluid storage tank. The controller isoperative to effect the circulation of the heat transfer fluid throughsaid second heat exchanger as a function of the temperature of the heattransfer fluid in said fluid storage tank.

There has thus been outlined, rather broadly, the more importantfeatures of the invention in order that the detailed description thereofthat follows may be better understood and in order that the presentcontribution to the art may be better appreciated.

Numerous objects, features and advantages of the present invention willbe readily apparent to those of ordinary skill in the art upon a readingof the following detailed description of presently preferred, butnonetheless illustrative, embodiments of the present invention whentaken in conjunction with the accompanying drawings. The invention iscapable of other embodiments and of being practiced and carried out invarious ways. Also, it is to be understood that the phraseology andterminology employed herein are for the purpose of descriptions andshould not be regarded as limiting.

As such, those skilled in the art will appreciate that the conception,upon which this disclosure is based, may readily be utilized as a basisfor the designing of other structures, methods and systems for carryingout the several purposes of the present invention. It is important,therefore, that the claims be regarded as including such equivalentconstructions insofar as they do not depart from the spirit and scope ofthe present invention.

For a better understanding of the invention, its operating advantagesand the specific objects attained by its uses, reference should be hadto the accompanying drawings and descriptive matter in which there isillustrated preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and objects other than those setforth above will become apparent when consideration is given to thefollowing detailed description thereof. Such description makes referenceto the annexed drawings wherein:

FIG. 1 is a schematic diagram of a system and apparatus for pre-heatingair in a forced draft heating system constructed in accordance with theprinciples of the present invention; and

FIG. 2 is a schematic diagram of the system and apparatus shown in FIG.1 with the inclusion of a heat recovery feature.

DETAILED DESCRIPTION OF THE PREFERED EMBODIMENTS

Reference will now be made in detail to the drawings. Wherever possible,the same reference numbers will be used throughout the drawings to referto the same or like elements.

With reference to FIG. 1 there is schematically shown a solar heatingsystem, generally designated by numeral 10, for use in combination witha forced draft heating system 100. The forced draft heating system 100can be any forced air heating system that is used to heat ventilationair. In general, the solar heating system 10 utilizes solar energy toheat or pre-heat ventilation air flowing through an air duct of theforced draft heating system 100 to reduce energy costs associated withoperating the forced draft heating system.

The forced draft heating system 100 is a typical heating systeminstalled in residential and commercial buildings to heat the interiorspace of the building by heating the ventilation air. For the purposeherein, the forced draft heating system 100 will be described generallyand generically as these systems are well known in the art. Further, theparticular construction or type of the forced draft heating system 100should not be construed as limiting as the solar heating system 10 ofthe present invention is operable with a wide range of different typesof forced draft heating systems, such as for example, heat pump systems,electric resistance heater systems and fuel-fired systems.

For the purpose of discussion, the forced draft heating system 100includes a housing containing an air handler 102 and a heat source 104.The air handler 102 operates to draw ventilation air from the buildinginto a return air duct 106 to be feed to the heat source 104 for heatingand to return the air to the building through an air discharge duct 108.The return air duct 106 and the air discharge duct 108 typically formpart of a more complex air distribution network of ducting, as such onlya portion of each ducting is shown for clarity. The forced draft heatingsystem further includes a controller 110 that function to control theoperation of the air handler 102 and the heat source 104. A thermostat112 is operably connected to the controller 110 and issues commandsignals to the controller to effect the operation of the air handler 102and the heat source 104. In one example, the heat source 104 is afuel-fired heat source. In this example, a flue 114 for carrying hotcombustion gases from the heat source extends upwardly from the housingof the forced draft heating system 100. Generally, in operation, the airhandling means 102 draws ventilation air to be heated from the spacethrough the air return duct 106 and into the housing where it isdirected through the heat source 104 and then discharged as heated airthrough the discharge duct 108 for delivery back to the space to beheated. The thermostat 112 monitors the space air temperature and issuesa command signal to the controller 110 to effect the operation of theheating system 1 00.

The solar heating system 10 of the present invention is designed to beintegrated with the forced draft heating system 100. The solar heatingsystem 10 is capable of providing an additional heat source to pre-heatventilation air flowing through the ducting of forced draft heatingsystem 100 and is also capable of being the primary heat source to heatthe ventilation air during low load conditions.

In doing so, the solar heating system 10 of the present invention,includes a solar energy collector assembly 12 that is positioned tocapture solar energy. Generally, the collector assembly 12 will bepositioned exteriorly to a building, such as for example on a roofsurface thereof. The collector assembly 12 includes one or more liquidtype solar energy collectors 13 which heat a liquid as it flows throughthe collector. The collector assembly 12 is positioned in a closed-loopflow path along with an insulated liquid storage tank 14 that contains aquantity of heat transfer fluid. A pump 16 is operated to circulate theheat transfer fluid from the storage tank 14 through the collector 12,where it is heated, and then returned back to the storage tank in aclosed-loop path 18. A second closed loop path 20 includes a second pump22 that is operated to circulate heated fluid from the storage tank 14through a heat exchanger 24 that is positioned within an air duct of theforced draft heating system 100 to heat ventilation air flowing throughthe duct. The air duct is preferably the return air duct 102 thatsupplies ventilation air to the forced heating system 100 to be heated.However, it is possible to position the heat exchanger 24 in any airduct forming part of the forced heating system 100.

The storage tank 14 can be provided with one or more heat sinks 26, suchas ceramic blocks or the like. The heat sinks 26 increase the heatstorage capacity of the solar heating system 10 by absorbing excess heatfrom the heat transfer fluid and then transferring the excess heat backto the heat transfer fluid when an opposite thermal gradient exists.

A controller 28 measures the temperature differential between the fluidin the collector assembly 12 by a first temperature sensor 30 and thefluid in the storage tank 14 by a second temperature sensor 32. When thetemperature of the fluid in the collector assembly 12 is higher than thetemperature of the fluid in the storage tank 14 by a first temperaturedifferential set-point, the controller 28 operates the pump 16 tocirculate the fluid from the storage tank through the collector assemblyto be heated. As the temperature of the fluid in the storage tank 14 israised, the temperature differential is reduced. Once a secondtemperature differential set-point is reached, the controller 28deactivates the pump 16 and the fluid is no longer circulated throughthe collector assembly 12. This operation ensures the highest efficiencyby circulating the fluid only during times where a beneficialtemperature differential exists. The first and second temperaturedifferential set points can be set during the initial install or duringmanufacture and may be made adjustable by an end user.

When the solar heating system 10 is integrated with a forced draftheating system 100 having a fuel-fired heat source 104, the solarheating system can include a heat recovery feature to recover waste heatfrom hot combustion gases, as shown in FIG. 2. The heat recover featureincludes a heat exchanger 30 positioned in or about the flow of hotcombustion gases exhausted from the heat source 104. The heat exchanger30 can be positioned about the flue 114 exhausting the combustion gasesor can be positioned within the flue to directly contact the combustiongases. For exemplary purposes only, the heat exchanger 30 can include aserpentine shaped tube wrapped around a length of the flue 114. Further,a heat insulating blanket 35 can be wrapped around the heat exchanger 30and the flue 114 to increase thermal efficiency.

The heat exchanger 30 is positioned in a third closed loop path 34 withthe fluid storage tank 14, thereby permitting circulation of the heattransfer fluid through the heat exchanger 30 where it is heated by hotcombustion gases exhausted from the heat source 104. The third closedloop path 34 may include it own separate pump (not shown) or can beconnected to the second pump 22 through a valve manifold 36. Themanifold 36 includes a first valve 38 for controlling the flow of fluidthrough the third closed loop path 34 and a second valve 40 forcontrolling the flow of fluid through the second closed loop path 20.The first and second valves 38, 40 could be replaced by a singleproportion valve (not shown) to proportion the flow fluid discharged bypump 22 between the second and third paths 20 and 34. The first andsecond valves 38, 40 are operably connected to the controller 28. Valve40 is a normally closed valve and valve 38 is a normal open valve.Generally, when the heat recovery feature is operational, the heattransfer fluid is prevented from flowing through the second closed path20, thereby preventing fluid from flowing through heat exchanger 24 thatmay have a lower temperature than the ventilation air that other wouldresult in cooling the ventilation air.

The thermostat 112 of the forced draft heating system 100 is connectedto the controller 28 in a bidirectional communication path and iscapable of sending and receiving information to and from the controller28. The thermostat 112 monitors the air temperature of the space to beheated and when the temperature drops below a set-point, the thermostat112 communicates with the controller 28 to determine the temperature ofthe heat transfer fluid in the fluid storage tank 14. Based upon thetemperature of the heat transfer fluid in the storage tank 14, thecurrent temperature of the air to be heated and the desired airtemperature, the thermostat 112 will issue command signals to thecontroller 28 and the controller 110 to operate in one of severaldifferent modes of operation. The thermostat 112 can be set to manuallyoperate in either of these modes or can be set to automatically operatein the mode which is most efficient for the current conditions.

In a first mode, ventilation air is heated by the circulation of heatedfluid through heat exchanger 24. In a second mode, ventilation air isheated by the circulation of heated fluid through the heat exchanger 24in tandem with the forced draft heating system 100. In a third mode,ventilation air is heated solely by the forced draft heating system 100and the heat recovery feature of the system 10 of the present inventionis operated to recover waste heat from hot combustion gases bycirculating the heat transfer fluid through heat exchanger 30. In afourth mode, ventilation air is heated solely by the forced heatingsystem 100.

In the first mode, where ventilation air is heated by the circulation ofheated fluid from the storage tank 14 through heat exchanger 24. Tooperate in this mode, the temperature of the heat transfer fluid in thestorage tank 14 must be above a first threshold and the temperaturedifferential between the actual temperature of the air in the spaced tobe heated and the desired temperature must be within a second threshold.If both of these conditions are met, the thermostat 112 will issue acommand signal to controller 110 to operate the air handling means 102to draw ventilation air into duct 106 and discharge the air through duct108. The thermostat 112 also issues a command signal to controller 28 tooperate pump 22 to circulate the heat transfer fluid through the heatexchanger 24. As the air is drawn through duct 106 it is passed acrossthe heat exchanger 24 where it is heated by the heat transfer fluid. Theair handling means 102 continues to draw the air into the housing of theforced draft heating system 100 and then discharges it through duct 108.The first mode will continue to operate until either the desiredtemperature of the air is reached or the temperature of the heattransfer fluid drops below the first threshold or the temperaturedifferential between the actual air temperature and the desired airtemperature exceeds the second threshold. In the later, operation willautomatically switch to another mode that is best suited to reduce thetemperature differential between the actual air temperature and thedesired temperature.

In the second mode, where ventilation air is heated by the circulationof heated fluid from the storage tank 14 through heat exchanger 24 intandem with the forced draft heating system 100. To operate in thismode, the temperature of heat transfer fluid in the storage tank 14 mustabove the first threshold and the temperature differential between theactual temperature of the air and the desired temperature of the air isoutside of the second threshold. If both of these conditions are met,the thermostat 112 will issue a command signal to controller 110 tooperate the heat source 104 and the air handling means 102. The airhandling means 102 draws air into duct 106 and across the heat source104 where it is then discharged through duct 108. The thermostat willalso issue a command signal to controller 28 to operate pump 22 tocirculate the heat transfer fluid through the heat exchanger 24. As theair flows through duct 106 it is passed across the heat exchanger 24where it is heated to a first temperature. The air then continues toflow across the heat source 104 where is it heated to a secondtemperature and then discharged through duct 108. This mode of operationwill continue to operate until either the desired temperature of the airis reached or the temperature of the heat transfer fluid drops below thefirst threshold. In the later, the thermostat 112 will issue a commandsignal to controller 28 to stop operation of pump 22 while the forceddraft heating system 100 continues to operate until the desiredventilation air temperature is met, which is the third mode ofoperation.

In the third mode of operation, where the heat recovery feature ofsystem 10 is active to recovery waste heat from hot combustion gasesexhausted by the operation of a fuel-fired heat source 104. To operatein this mode, the temperature of heat transfer fluid in the storage tank14 is below the first threshold and the force draft heating system 100must be a fuel-fired system. In this mode, thermostat 112 communicatedto controller 28 that the forced draft heating system 100 isoperational. Controller 28 then operates to open valve 34 and closevalve 36 and pump 22 to circulate heat transfer fluid from the storagetank 14 through heat exchanger 30 where it is heated by the hotcombustion gases exhausted from the heat source 104.

In the forth mode, where the forced draft heating system 100 is operatedalone to heat ventilation air. In other words, heat transfer fluid isnot circulated from the storage tank 14 through heat exchanger 24. Theventilation air is heated solely by the heat source 104 of the forceddraft heating system.

A number of embodiments of the present invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

1. A solar heating system for use with a forced draft heating system forheating ventilation air of a building, where the forced draft heatingsystem includes an air handler, a heat source, a return air duct, an airdischarge duct and a thermostat that controls the operation or theforced heating system, the solar heating system comprising: a solarcollector assembly which heats a liquid as it is circulated therethroughby solar radiation; a fluid storage tank for containing a quantity ofheat transfer fluid; a first heat exchanger positionable in an air ductof the forced draft heating system such that air flowing through theduct is caused to flow across said first heat exchanger; said solarcollector assembly is in fluidic communication with said fluid storagetank such that heat transfer fluid contained therewithin can becirculated through said solar collector assembly and returned to saidstorage tank; said first heat exchanger is in fluidic communication withsaid fluid storage tank such that heat transfer fluid containedtherewithin can be circulated through said first heat exchanger andreturned to said storage tank; a controller; said controller operativeto effect the circulation of the heat transfer fluid through said solarcollector assembly as a function of a temperature differential betweenthe heat transfer liquid in said solar collector assembly and the heattransfer liquid in said fluid storage tank; and said controlleroperative to effect the circulation of the heat transfer fluid throughsaid first heat exchanger as a function of the temperature of the heattransfer fluid in said fluid storage tank, the temperature of the air tobe heated, and the desired temperature of the air to be heated.
 2. Thesolar heating system of claim 1, wherein the duct of the forced draftheating system is the return air duct.
 3. The solar heating system ofclaim 1, further comprising: one or more heat sinks positioned to be inheat transfer communication with the heat transfer liquid containedwithin said fluid storage tank.
 4. The solar heating system of claim 3,wherein said one or more heat sinks is positioned within said fluidstorage tank.
 5. The solar heating system of claim 1, furthercomprising: a second heat exchanger positionable in the flow of hotcombustion gases exhausted by the heat source of the forced draftheating system, wherein said second heat exchanger is in fluidiccommunication with said fluid storage tank such that the heat transferfluid contained within said fluid storage tank can be caused tocirculate through said second heat exchanger and returned to said fluidstorage tank; and said controller operative to effect the circulation ofthe heat transfer fluid through said second heat exchanger as a functionof the temperature of the heat transfer fluid in said fluid storagetank.
 6. The solar heating system of claim 1, wherein said solarcollector assembly is in fluidic communication with said fluid storagetank in a first closed loop flow path; and wherein said first heatexchanger is in fluidic communication with said fluid storage tank in asecond closed loop flow path.
 7. The solar heating system of claim 6,wherein said first and second closed loop flow paths are separate fromeach other.
 8. The solar heating system of claim 7, further comprising:a first pump in said first closed loop flow path for circulating theheat transfer liquid through said solar collector assembly; a secondpump in said second closed loop flow path for circulating the heattransfer liquid through said first heat exchanger; and said controlleroperatively connected to said first pump to effect the circulation ofthe heat transfer fluid through said collector assembly and operativelyconnected to said second pump to effect the circulation of the heattransfer fluid through said first heat exchanger.